Make PendingTask move-only and pass it by value on retaining params

base/pending_task.h

Index: base/pending_task.h
diff --git a/base/pending_task.h b/base/pending_task.h
index c31ab9af264745c19042267d52aa0646edd83cb9..5761653397e0e5d011522f56e786fa1cbbbcc373 100644
--- a/base/pending_task.h
+++ b/base/pending_task.h
@@ -19,14 +19,16 @@ namespace base {
 // for use by classes that queue and execute tasks.
 struct BASE_EXPORT PendingTask : public TrackingInfo {
   PendingTask(const tracked_objects::Location& posted_from,
-              const Closure& task);
+              Closure task);
   PendingTask(const tracked_objects::Location& posted_from,
-              const Closure& task,
+              Closure task,
               TimeTicks delayed_run_time,
               bool nestable);
-  PendingTask(const PendingTask& other);
+  PendingTask(PendingTask&& other);
   ~PendingTask();
 
+  PendingTask& operator=(PendingTask&& other);
+
   // Used to support sorting.
   bool operator<(const PendingTask& other) const;